This invention generally relates to systems and methods for sensing when an aircraft is approaching a volcanic plume. As used herein, the term “volcanic plume” encompasses a cloud of volcanic ash suspended in a mass of gas that may include volcanic gases.
Volcanic plumes present two problems for aircraft: (a) engine shutdown due to ash; and (b) aircraft damage and/or crew and passenger injury due to ash and corrosive gases. Volcanic ash comprises tiny jagged particles of rock and natural glass blasted into the air by a volcano. Wind can carry ash thousands of miles, affecting far greater areas than other volcano hazards. Volcanic ash particles are extremely abrasive. They are jagged particles of rock and glass that can cause rapid wear to the internal workings of jet engines. More important, high temperatures in some parts of jet engines can melt the ash; it then re-solidifies on cooler parts of the engine, forming a layer that blocks airflow, interferes with moving parts, and eventually shuts down the engine.
Another issue is the potentially harmful effects of elevated concentrations of SO2 and sulfate aerosol in ash-poor clouds on aircraft and avionics. In addition, volcanic ash particles, with sulfuric acid adhered thereto, are tiny enough to travel deep into the lungs of human beings, which may be harmful and potentially fatal to people.
Pilots are advised to avoid visible volcanic plumes. This is not always possible. Diffuse volcanic ash is hard to distinguish from smoke or thin cirrus. On moonless nights, volcanic ash may be invisible. Airborne weather radar is no help because ash particles have virtually no radar signature. Onboard laser scattering instruments work reasonably well at detecting volcanic ash, but such instruments are heavy, increase drag, and give no advance warning before the airplane is actually flying through a volcanic plume.
The overall technical problem is to provide means for detecting airborne volcanic ash at cruise altitude and then alerting aircraft so they can avoid damage or injury from passage through the volcanic plume. General approaches to solving the specific technical problem of detecting the presence of volcanic ash particles in the atmosphere surrounding an aircraft include at least the following:
1. See and Avoid. In daytime clear weather, pilots can see and avoid the visually distinctive cloud from an erupting volcano.
2. Geological Reports. For volcanoes that are well monitored, sensors or people on the ground can quickly observe an eruption and report it to flight safety authorities such as the FAA. In these cases, a notice to airmen is issued.
3. Satellite Observations. A few satellites are capable of detecting volcanic plumes from orbit, based on the sulfur dioxide spectra, the thermal infrared emission, visible volcanic plumes, or a combination of these. When a satellite detects a volcanic plume, a notice to airmen is issued.
4. Plume Forecasts. Given geological reports or satellite observations, the national weather services of various countries predict where the volcanic plume will go at various times. Operators use these forecasts to choose safe routes.
5. Radio-Frequency Occultation. Volcanic emissions of hydrogen sulfide have refractive effects on radio signals from satellites. The effects can be detected and used to warn aircraft of volcanic
The drawbacks of the foregoing approaches are as follows:
1. See and Avoid. Volcanic plumes are often encountered during nighttime and/or embedded within other clouds. Therefore, visual detection is not always effective.
2. Geological Reports. Many remote volcanoes around the world are still not well instrumented and can erupt without immediate detection. Even after detection, the mechanism to issue a notice to airmen imposes a delay for processing and distribution, during which an unwarned aircraft may encounter the plume.
3. Satellite observations are not continuous. An eruption that occurs between satellite passes may go undetected for 6 to 12 hours, which is more than enough time for aircraft to encounter the plume. The period of non-detection may go on longer for small eruptions or during overcast conditions. Even after detection, the mechanism to issue a notice to airmen imposes a delay for processing and distribution, during which an unwarned aircraft may encounter the plume.
4. Plume forecasts have large margins of error, so regulators impose large keep-out zones around the most likely plume location, especially at night. Aircraft may fly 100 miles farther out of their way than necessary because of uncertainties in the forecasts. This costs passengers time and costs operators money.
5. Radio-frequency (RF) occultation requires specialized RF receivers. Not all aircraft operators may be able to afford them. Further, it does not detect thin clouds of volcanic ash: essentially all volcanic gases dissipate from the ash after a few days.
It would be desirable to provide means for remotely visually detecting airborne volcanic ash at cruise altitudes without the above-described drawbacks.